As .beta.-oxo-.beta.-benzenepropanethioamide derivatives, there have been known N, .alpha., .alpha.-trimethyl-.beta.-oxobenzenepropanethioamide (Compound of the following formula (A)) and N-phenyl-.alpha., .alpha.-dimethyl-.beta.-oxobenzenepropanethioamide (Compound of the following formula (B)) (Bull. Soc. Chim., Fr., 1975, 829), and as the .alpha.-monomethyl derivatives thereof, there have been known the N-propyl derivative (Compound of the following formula (C)) (Tetrahedron 44, 3159(19)), the N-phenyl derivative (Compounds of the following formulas (D) and (E)) (J. Chem. Soc. Perkin I, 1988, 1739) and 4-(2-methyl-3-oxo-3-phenyl-1-thioxopropyl) morpholine (Compound of the following formula (F)) (Synthesis 1988, 556), but none of the pharmaceutical actions thereof has been reported yet. ##STR1## (In the above formulas, Me represents methyl group; nPr represents n-propyl group; and Ph represents phenyl group.)
Alternatively, a variety of compounds having anti-hypertensive action have been proposed, and it has been known, for example, that thioformamide derivatives having a heterocyclic ring such as pyridine and quinoline have an ability to lower the arterial pressure in spontaneous hypertensive rats (SHR) (see Japanese Patent Laid-open Nos. 130974/1980, 42687/1982, 7188/1984, 232281/1984, 211566/1989, 30875/1989, and 273/1990).